Mark Udall
and Ron Wyden, both members of the Senate intelligence committee,
said they were not convinced by the testimony of the NSA director,
General Keith Alexander, on Capitol Hill on Wednesday, who claimed
that evidence
gleaned from
surveillance helped thwart attacks in the US.

"We have not yet seen any evidence showing that the NSA's dragnet
collection of Americans' phone records has produced any uniquely
valuable intelligence," they said in a statement released on
Thursday ahead of a widely anticipated briefing for US senators
about the National Security Agency's activities.

"When you're talking about important liberties that the American
people feel strongly about, and you want to have an intelligence
program, you've got to make a case for why it provides unique value
to the [intelligence] community atop what they can already have,"
Wyden, an Oregon Democrat, told the Guardian in an interview on
Thursday.

Alexander testified before the Senate appropriations committee
that maintaining a database of millions of Americans' phone records
was critical to thwarting "dozens" of plots.
One of the examples Alexander mentioned, the case of would-be
New York subway bomber Najibullah Zazi, appears to have been
prevented by conventional police surveillance, including efforts by
UK investigators.

"Gen Alexander's testimony yesterday suggested that the NSA's
bulk phone records collection program helped thwart 'dozens' of
terrorist attacks, but all of the plots that he mentioned appear to
have been identified using other collection methods," Wyden and
Udall said in a statement. "The public deserves a clear
explanation."

Alexander testified that the efficacy of the phone-records
program could not be independently analysed from that of another NSA
program disclosed by the Guardian, an
effort called Prism that monitors the internet communications of
people believed to be outside the US. In an interview with the
Guardian, Wyden challenged that assertion as well.

"I have real reservations that the argument that they can't be
evaluated separately," Wyden said. "If a program provides unique
value, the people running it ought to explain it. I'm certainly open
to doing that in a classified setting, and I know of a program where
they haven't done it."

Wyden said he could not elaborate on what that program is, citing
its classified nature.

Alexander also testified that the databases of Americans' phones
records contains safeguards governing its searchability to prevent
the NSA from abusing it. But there is ambiguity about whether a
court or any outside body must grant the NSA permission to search
it.

"If they claim that this program has lots of safeguards, wouldn't
you expect they would detail them – 'Here are the procedures for
following up on an individual'?" Wyden said. "This is certainly an
issue I have a strong interest in."

Wyden had earlier
challenged the truthfulness of Alexander's nominal boss, James
Clapper, the director of national intelligence. Photograph: Saul
Loeb/AFP/Getty Images

The direct challenge to the NSA's veracity comes ahead of a
closed-door session in the Capitol for senators to hear from
Alexander directly about the details and the effects of the program.
And it follows on an earlier challenge by Wyden to the truthfulness
of Alexander's nominal boss, James Clapper, the director of national
intelligence.

In March, Clapper responded "no" and "not wittingly" to a
question from Wyden about whether the NSA collects "any type of data
at all on millions or hundreds of millions of Americans." Clapper
has since admitted that was the "least untruthful" answer he
could have given.

Wyden pointed out that the reason he asked that question was
because of an assertion Alexander made publicly at a hacker
conference in July. Alexander said at the Defcon conference in Las
Vegas that the NSA only collected data on Americans "incidentally,
in targeting a bad guy" and that "the story we have millions or
hundreds of dossiers on people is absolutely false".

"In the last day I've been struck by many people who don't want a
vigorous debate, saying that somehow this discussion started on
Capitol Hill," Wyden said. "This was started by General Alexander's
comment in a public forum. That's why I think now we're going to
have some public hearings."

Other senators who have been critical of the NSA looked forward
to Thursday afternoon's closed-door briefings.

"Sen Udall is planning on attending the briefing as long as it
does not conflict with markup/votes on the Senate armed services
committee," Udall spokesman Mike Saccone said in an email to the
Guardian.

"Sen Udall hopes he and his colleagues get specific answers out of
Gen Alexander on what appears to be a discrepancy between what he
told the appropriations committee yesterday [Wednesday] and the
information previously provided to the intelligence committee."

Jamal Raad, a spokesman for senator Jeff Merkley, an Oregon
Democrat, said: "Senator Merkley wants a clear answer to his
question on how the Fisa court has interpreted the language of the
law. The administration should then commit to release those
interpretations to the American public in order to have a full
debate."